The shortest wavelength of X-rays emitted from an X-rays tube depends upon

Nature of the gas in the tube Voltage applied to tube Current in the tube Nature of target of the tube

Voltage applied to tube

$eV = \frac{hc}{λ}$ $ or \, λ= \frac{hc}{eV}$ ie , $ λ ∝ \frac{1}{V}$